(1) Microbial Pesticides
Bacillus thuringiensis (B.t.) produces an insect toxin designated as .delta.-endotoxin. It is synthesized by the B.t. sporulating cell. The toxin, upon being ingested in its crystalline form by susceptible insect larvae, is transformed into biologically active moieties by the insect gut juice proteases. The primary target is insect cells of the gut epithelium, which are rapidly destroyed.
The reported activity spectrum of B.t. covers insect species within the order Lepidoptera, many of which are major pests in agriculture and forestry. The activity spectrum also includes the insect order Diptera, which includes mosquitos and black flies. See Couch, T. L. (1980) "Mosquito Pathogenicity of Bacillus thuringiensis var. israelensis," Developments in Industrial Microbiology 22:61-76; Beegle, C. C., (1978) "Use of Entomogenous Bacteria in Agroecosystems," Developments in Industrial Microbiology 20:97-104. B.t. isolates also have been shown to be active against beetles in the order coleoptera.
(2) Lepidopteran Pests
The diamondback moth Plutella xylostella (DBM) is a lepidopteran pest on cruciferous plants. The small larvae are foliar feeders that chew holes in the leaves. This can result in severe damage when populations are high. In addition to all the cruciferous vegetable crops, such as cabbage, broccoli, bok-choy, and cauliflower, DBM also attacks certain ornamental and greenhouse plants such as stocks, sweet alyssum, wallflower, and candytuft.
DBM is widely distributed and is found virtually wherever its host plants are grown. In the United States, Central America, Europe, and Asia, it is a major pest of crucifers. In many of these areas, it has become the most important pest, since it has developed resistance to chemical insecticides and cannot be effectively controlled. In these areas there is a desperate need for alternative control strategies. Bacillus thuringiensis has been somewhat effective in the past, but newer and more potent strains tailored to this species could substantially improve efficacy and fill an important need in managing this species.